1. Field of the Invention
The present invention relates to a thermal transfer printer and more particularly to a method for setting a desired color of a color ink ribbon in a thermal transfer printer.
2. Description of the Prior Art
FIG. 3 illustrates a conventional printer in which a flat plate-like platen 2 is disposed nearly centrally on a frame 1 of the printer so as to be approximately perpendicular to a printing surface. A carriage shaft 3 is disposed in parallel with the platen 2 in a lower position in front of the platen 2 of the frame 1. The front edge of the frame 1 is formed with a flange-like guide portion 4, and on the carriage shaft 3 and the guide portion 4 there is mounted a carriage 5 reciprocably movable along the carriage shaft 3 and the guide portion 4. To the front end of the carriage 5 is attached a printing head 6 in an opposed relation to the platen 2. A ribbon cassette (not shown) which contains an ink ribbon and which guides the ink ribbon to the space between the printing head 6 and the platen 2 is to be loaded onto the upper surface of the carriage 5.
In addition, a winding mechanism 7 is disposed in the carriage 5. The winding mechanism 7 has a winding shaft 8, as shown in FIGS. 4 and 5. The lower end of the winding shaft 8 is integrally formed with an externally projecting support flange 9, and a winding gear 10 is loosely fitted on the lower end portion of the winding shaft 8 so as to be rotatable independently of the winding shaft. Felt 11, serving as a slip mechanism, is interposed between the underside of the winding gear 10 and the support flange 9 of the winding shaft 8. Further, a winding bobbin 12 is fixed onto the upper end portion of the winding shaft 8 so that it is exposed from the upper surface of the carriage 5 for engagement with a winding hole (not shown) of the ribbon cassette. From the outer peripheral surface of the winding bobbin 12 there are projected three engaging pawls 13 in circumferentially trisected positions. In the underside of the winding bobbin 12 there is formed an annular retaining slot 14. On the outer peripheral side of the winding shaft 8 there is disposed a spring 15 whose upper end is retained in the retaining slot 14 of the winding bobbin 12 and whose lower end is in abutment with the upper surface of the winding gear 10. By virtue of the spring 15, the winding gear 10 is brought into pressure contact with the support flange 9 of the winding shaft 8 through the felt 11.
Meshing with the winding gear 10 is a driving gear 18 fixed onto a rotary shaft 17 of a ribbon winding motor 16. The driving gear 18 is rotated by the ribbon winding motor 16 to rotate the winding gear 10, so that this rotative driving force is transmitted to the winding shaft 8 by a frictional force of the felt 11 created by virtue of the spring 15 on the winding gear 10.
Behind the platen 2 there is formed a paper inlet 19 for feeding paper (not shown) forwardly of the platen 2. In the paper inlet 19 portion there are disposed paper feed rollers 20 for feeding the paper at a predetermined speed, and under the paper feed rollers 20 there are rotatably disposed pressure rollers 21 in pressure contact with the feed rollers 20. The paper inserted from the paper inlet 19 is conveyed while being sandwiched between the feed rollers 20 and the pressure rollers 21.
In the above conventional printer, paper is inserted from the paper inlet 19 and sandwiched between the paper feed rollers 20 and the pressure rollers 21. Rollers 20 are rotated by the stepping motor to feed the paper at a predetermined speed in a direction perpendicular to the moving direction of the carriage 5. At the same time, the carriage 5 is driven and the ribbon winding motor 16 is also driven to rotate the winding shaft 8 through the winding gear 10, whereby the winding bobbin 12 is rotated to wind up an ink ribbon from the ink ribbon cassette. In this condition, the printing head 6 is driven in accordance with a desired print signal to make a desired printing for the paper.
In the case where a multi-color ink ribbon of plural colors is used as the ink ribbon contained in the ribbon cassette, markers 23 of different longitudinal sizes are provided at boundary portions of the colors, e.g. yellow (Y), magenta (M) and cyan (C), of the ink ribbon indicated at 22, as shown in FIG. 6. The colors of the ink ribbon 22 are detected by reading the markers 23 while winding up the ink ribbon 22 under operation of the ribbon winding motor 16 and hence rotating of the winding bobbin 12 in the same manner as in the foregoing ink ribbon winding operation.
Upon detection of a desired color, the ribbon winding motor 16 is further driven to feed the ribbon so that the desired color reaches a position opposed to a printing position.
In the above conventional color ribbon searching method, however, the diameter of the ribbon on the winding bobbin 7 side becomes different from the original diameter (becomes larger) as the ink ribbon is used, so the amount of the ink ribbon wound up also becomes different even if the winding motor 16 is rotated by the same amount (the same number of steps). More particularly, the amount of ribbon fed from the position of a ribbon color detecting sensor becomes different as the ribbon is used. It is therefore necessary to preset the amount of rotation of the winding motor 16 to wind up the ink ribbon such that a desired color is sure to be opposed to the printing position in a less woundup state on the winding bobbin 7 side (that is, at the beginning of use of the ink ribbon). Where such setting is made, however, the amount of the ink ribbon becomes large even in a somewhat used state of the ribbon and thus the ribbon is wasted. This amount of ink ribbon wasted increases in with increase the winding-side diameter of the ribbon. In order to eliminate such waste of the ribbon, there has been proposed a method in which the head 6 is pressed against the platen as in the ordinary printing, and then the ribbon is drawn out by utilizing the pressing force of the head and is fed by the same distance as the amount of movement of the carriage 5 (head) by utilizing the slip mechanism of the winding bobbin. According to this method, however, it is necessary to move the carriage 5 even when printing is not performed, and thus takes time for feeding the ribbon.